Development of familial and sporadic Alzheimer's Disease (FAD and SAD) therapies requires deeper understanding of disease initiation and progression. A key unanswered question is whether all FAD and SAD neuronal misbehavior is solely the result of processes initiated or enhanced by secreted Amyloid Precursor Protein (APP) fragments such as A and sAPP (and therefore cell non-autonomous), or whether A- independent intracellular processes driven by APP proteolytic products, e.g., the C-terminal fragment (CTF) (and therefore potentially cell autonomous) processes are a major contributor. Specifically, the major hypothesis for AD initiation and progression is the amyloid cascade hypothesis, which proposes that Ass peptide fragments of human APP are necessary and sufficient to initiate and to drive all downstream pathologies typical of AD progression including synaptic defects [1]. Alternative ideas include intracellular defects caused by presenilin or APP mutants/fragments that generate defects in endosomal or lysosomal pathways, axonal transport, neurotrophic signaling, transcriptional control, cell cycle reinitiation, oxidative defets, etc. [2-7]. There are also two-hit models in which A is part of an initiating or enhancing insult n combination with intracellular insults [8-11]. These three types of models (autonomous, non-autonomous, two- hit) make distinct experimental predictions for mixed cell culture experiments using neurons derived from human induced pluripotent stem cells (hIPSC). For example, the (non-autonomous) amyloid cascade hypothesis, and related non-autonomous hypotheses based on toxicity of secreted fragments of APP (or other molecules) predict that mixtures of diseased and non-diseased neurons should cause disease phenotypes in the non-diseased neurons owing to secretion of toxic products by diseased neurons. Alternatively, in cell autonomous models of AD that do not posit secretion of toxic products, mixtures of diseased and non-diseased neurons should not lead to disease phenotypes in non-diseased neurons. Finally in two hit models, cell autonomous processes and cell nonautonomous processes might combine such that cell autonomous initiation of phenotypes might be enhanced by A or other secreted toxic mediators. We propose to begin testing these ideas by further developing a new platform hIPSC human neuronal model of AD. These investigations, if successful, can shed new light on the relative contributions of autonomous and non-autonomous processes and two-hit models. We will use neurons made from hIPSC lines derived from a non-demented control patient (NDC), an FAD APPDp patient, and an SAD patient (called SAD2). We have two specific experimental aims: Aim 1) To test the hypothesis that some or all defects observed in purified neurons containing either an FAD APP duplication or a genome from an individual with SAD called SAD2 are cell-autonomous. Aim 2) To test the hypothesis that astrocytes carrying different ApoE alleles enhance or suppress AD phenotypes in purified neurons. PUBLIC HEALTH RELEVANCE: Alzheimer's Disease is a major public health problem that develops in as much as 10% of the population older than 65 and 50% of the population older than 85. There are currently no disease altering therapeutic strategies although some agents offer temporary symptomatic relief. We propose to use stem cell technology to discover neuronal mechanisms that cause Alzheimer's Disease with the hope that this work will allow new therapeutics and predictive diagnostics to be developed.